Pneumatic booster

Abstract

The invention relates to a pneumatic brake-booster comprising a casing (10), inside which is situated a piston (22) consisting of a rear tubular part (22) which supports a skirt (14) and which with the aid of an unwinding diaphragm (12) defines a front chamber (16) permanently connected to a vacuum source and a rear chamber (18) selectively connected to the front chamber (16) or to the atmosphere by a valve mechanism (20a, 32a, 40) actuated by a control rod (34) adapted to bear, by way of a plunger (32) sliding in a bore (30) of the piston (20), against one face of a reaction disk (58) fastened to a push rod (56), the valve mechanism (20a, 32a, 40) comprising a valve closure member (40) cooperating with a first valve seat (32a) formed on the plunger (32) and with a second valve seat (20a) formed on the piston (20 ), a retaining member (50), for the plunger (32) disposed in a radial space (38) in the piston (20) and having an inner end region extending the bore (30) of the piston (20) and forming a stop surface cooperating with axial abutment with a shoulder (74) on the plunger (32). According to the invention, the stop member (50) is permanently urged towards the rear by a resilient mechanism (66) to act in the closing direction on a second valve mechanism (64, 78).

We claim: 
     
       1. A pneumatic brake-booster, comprising a casing inside which is situated a piston comprising a rear tubular part which supports a skirt and which with a diaphragm defines a front chamber under low pressure and a rear chamber connected selectively to one of said front chamber and atmosphere by first valve means actuated by a control rod adapted to bear, by means of a plunger sliding in a bore of said piston, against one face of a reaction disk adjacent a push rod, said first valve means comprising a first valve closure member cooperating with a first valve seat at said plunger and with a second valve seat at said piston, a stop member for said plunger disposed in a radial space in said piston and having an inner end region extending into said bore of the piston and forming a stop surface cooperating by axial abutment with a first shoulder on said plunger, wherein said stop member is urged permanently rearwardly by resilient means in order to urge second valve means in a closing direction, said second valve means comprising a second valve closure member cooperating with a third valve seat at said piston. 
     
     
       2. The booster according to claim 1, wherein said second valve closure member is formed on said stop member. 
     
     
       3. The booster according to claim 2, wherein said second valve means may be urged in an opening direction by abutment of said inner end region of said stop member against a second shoulder of said plunger. 
     
     
       4. The booster according to claim 3, wherein in an open position said second valve means permits communication between said rear chamber of the booster and the atmosphere. 
     
     
       5. The booster according to claim 4, wherein opening of said second valve means is determined by an axial distance between said first and second shoulders of said plunger. 
     
     
       6. The booster according to claim 5, wherein the opening of said second valve means is effected when said plunger has made, relative to said piston, a stroke whose length is greater than said axial distance between said first and second shoulders of said plunger. 
     
     
       7. The booster according to claim 6, wherein the opening of said second valve means comprises pivoting of said stop member about a pivoting axis located at a right angle to a direction of the sliding of said plunger in said piston. 
     
     
       8. The booster according to claim 7, wherein said pivoting axis of said stop member comprises an anchorage area of an outer end region of said stop member on a part fastened to said piston. 
     
     
       9. The booster according to claim 8, wherein a stroke effecting the opening of said second valve means is made by said plunger when an action corresponding to heavy braking is applied to said control rod.